The present invention generally relates to management information updating methods and mass storage systems and, more particularly, to a management information updating method for updating management information which is managed by a host unit of a computer system when storing and retrieving a storage medium with respect to a mass storage system which is used as an external storage of the computer system, and to a mass storage system which employs such a management information updating method.
Recently, the amount of information processed in a computer system has increased considerably. For this reason, various automated mass storage systems have been proposed. The mass storage system stores storage mediums which contain the information, and the storage mediums are stored in and retrieved from the mass storage system without any need of operator intervention.
The storage medium takes the form of a magnetic tape cartridge, an optical disk cartridge or the like. The mass storage system has accommodating shelves which are provided with a plurality of cells for storing a plurality of storage mediums. An access mechanism of the mass storage system includes a mechanical hand which is used to store the storage medium into the cell and to retrieve the storage medium from the cell. The mechanical hand also transports the retrieved storage medium to a recording/reproducing unit which writes/reads data to/from the storage medium.
When the data write/read is completed, the mechanical hand retrieves the storage medium from the recording/reproducing unit and transports the storage medium to the cell to be stored therein. If the host unit instructs the mass storage system that a storage medium has become unnecessary, the mechanical hand transports the unnecessary storage medium to a load/eject mechanism so that the operator may retrieve the unnecessary storage medium which is ejected. On the other hand, if the operator loads a storage medium into the load/eject mechanism, the mechanical hand transports the loaded storage medium to the recording/reproducing unit or to the cell to be stored therein. Therefore, the mass storage system functions as a type of automated storehouse.
The host unit stores management information which is necessary to manage the storage mediums (i.e., media) including moving the storage mediums in the above described manner. For this reason, the management information is updated every time the operator stores or retrieves the storage medium.
While the management information is being updated, the host unit cannot access the mass storage system, and the processing efficiency of the computer system is deteriorated thereby. Hence, it is essential that the update time required to update the management information be short.
In FIG. 1A shows a plan view of a conventions mass storage unit 10 and FIG. 1 (B) shows a side view of the mass storage unit 10.
In FIGS. 1A and 1B, a cell drum 1 has a plurality of rotatable shelves 1a, 1b, 1c, which are arranged in a cylindrical shape. Each shelf of the cell drum 1 includes a plurality of cells 6 for storing storage mediums 5. For the sake of convenience, it will be assumed that the storage mediums 5 are magnetic tape cartridges. Each cell 6 stores one magnetic tape cartridge 5, and the cells 6 of the shelves are aligned at each level of the cell drum 1 in the horizontal direction in FIG. 1 (B) and aligned in each column of the shelves along the vertical direction in FIG. 1 (B).
An accessor 2 is arranged in correspondence with one column of the shelves of the cell drum 1. The accessor 2 detects whether or not a magnetic tape cartridge 5 exists within a cell 6, and also transports a magnetic tape cartridge 5 between corresponding cells 6 and the drive units 7 and 8 which perform data recording/reproduction with respect to the magnetic tape cartridge 5. The accessor 2 includes a mechanical hand 3 which transports the magnetic tape cartridge 5, fingers 4 which hold the magnetic tape cartridge 5, and a motor M1 which drives the mechanical hand 3 and the fingers 4.
A normally closed door 9 is provided in correspondence with one column of the shelves of the cell drum 1. The width of the door 9 is such that the operator can store and retrieve the magnetic tape cartridge 5 with respect to the cells 6 which are arranged in one column of the shelves of the cell drum 1.
The cell drum 1 is rotatable in directions A and B by a motor M2. The cell drum 1 is rotated in either the direction A or B and stopped at a position where the accessor 2 confronts the cell 6 which stores the specified magnetic tape cartridge 5 which is to be transported.
The mechanical hand 3 of the accessor 2 is moved in a direction C or D and positioned at the cell 6 which stores the specified magnetic tape cartridge 5. Then, the fingers 4 of the mechanical hand 3 are inserted into the cell 6 to hold and extract the specified magnetic tape cartridge 5 from, and transport some outside, the cell 6. The retrieved magnetic tape cartridge 5 is transported to the drive unit 7 or 8 and set therein.
When the data recording/reproduction in the drive unit 7 or 8 is completed, the fingers 4 of the mechanical arm 3 extract the magnetic tape cartridge 5 from the drive unit 7 or 8. In addition, the cell drum 1 is rotated so that the specified cell 6 in which the magnetic tape cartridge 5 is to be stored confronts the accessor 2. Thereafter, the mechanical hand 3 is positioned at the specified cell 6, so that the fingers 4 can store the transported magnetic tape cartridge 5 into the specified cell 6.
FIGS. 2A and 2B are is a diagram for explaining the storage and retrieval of a magnetic tape cartridge 5 with respect to a cell 6. FIG. 2A is a general plan view of the mass storage unit 10, and FIG. 2B is general side view of the mass storage unit 10.
The operator may wish to load a new magnetic tape cartridge 5 into the mass storage unit 10 or unload the magnetic tape cartridge 5 from the mass storage unit 10. In this case, the operator transmits a command from the host unit and sets the operation mode of the mass storage unit 10 to a load/eject mode. In addition, the operator manipulates a shelf selection switch 11 to rotate the cell drum 1. The host unit forms a mass storage system together with the mass storage unit 10.
The operator monitors a display panel (not shown) or the like, and manipulates the shelf selection switch 11 to stop the rotation of the cell drum 1 when the operator recognizes that a desired cell column 15 has come to the position confronting the door 9.
Then, the operator manipulates a door open switch 12 to open the door 9. Hence, the operator can store the new magnetic tape cartridge 5 into the cell 6 in the desired cell column 15 or retrieve the magnetic tape cartridge 5 from the cell 6 in the desired cell column 15. In this state, the mass storage unit 10 invalidates the signal from the shelf selection switch 11 which is manipulated in response to the signal which is received from the door open switch 12 when this door open switch 12 is manipulated.
When the storage or retrieval of the magnetic tape cartridge 5 with respect to the desired cell column 15 is completed, the operator closes the door 9. The closed state of the door 9 is detected by a sensor 14, and the sensor 14 outputs a signal indicative of the closed state of the door 9. Hence, the mass storage unit 10 validates the signal from the shelf selection switch 11 in response to the output signal of the sensor 14. The operator can then rotate the cell drum 1 so that a next desired cell column 15 moves to the position confronting the door 9, and it is possible to sucessively store or retrieve the magnetic tape cartridge 15 with respect to this next desired cell column 15.
After the storage or retrieval of the magnetic tape cartridge 5 ends, the operator manipulates an end switch 13 to notify the end of the load/eject mode to the mass storage unit 10. The mass storage unit 10 notifies the end of the load/eject mode to the host unit, and the host unit updates the management information.
Next, a description will be given of an example of the management information (cell address information), by referring to FIG. 3.
FIG. 3 shows a case where the cell drum l of the mass storage unit 10 has 9 cell columns 15 and 35 shelves are stacked in each cell column 15. Hence, there are 315 cells 6 in this case. The cell 6 in which the magnetic tape cartridge 5 is stored and the cell 6 in which no magnetic tape cartridge 5 is stored can be distinguished by the column numbers "0" through "8" and the shelf number "0" through "34".
At the time of the initial setting, the host unit investigates the column number and the shelf number of the cell 6 in which the magnetic tape cartridge 5 is stored by the operator, and forms management (address) information indicative of the respective cells 6 which store the magnetic tape cartridges 5.
In other words, when the mass storage unit 10 notifies the end of the load/eject mode, the host unit instructs the mass storage unit 10 to rotate the cell drum 1 and to stop the cell drum 1 at a position such that the cell column 15 having the column number "0" confronts the accessor 2. Thereafter, the host unit instructs the mass storage unit 10 to position the mechanical hand 3 to the cell 6 having the shelf number "0", and instructs the fingers 4 to enter within the cell 6 and hold (i.e., engage, or grasp) the magnetic tape cartridge 5 which is stored in this cell 6.
If the fingers 4 can hold the magnetic tape cartridge 5 within the cell 6, the mass storage unit 10 judges that the magnetic tape cartridge 5 exists within this cell 6. In this case, a bar code reader (not shown) which is provided on one of the finger, 4 reads a bar code on the magnetic tape cartridge 5 and transfers the read bar code to the host unit. As indicated by hatchings in FIG. 3, the host unit stores this bar code at the cell position having the column number "0" and the shelf number "0".
The host unit controls the mass storage unit 10 so as to repeat the above described operations, and thus to search for the magnetic tape cartridges 5 stored in the cells 6 having the column number "0" and the shelf numbers "1" through "34". The host unit next instructs the mass storage unit 10 to rotate the cell drum 1 when the writing of the bar code to the respective cell position, where the fingers 4 of the mechanical hand 3 were able to hold the magnetic tape cartridge 5, for each cell of column "0" is completed. In addition, the host unit controls the mass storage unit 10 to similarly search for the magnetic tape cartridges 5 stored in the succession of respective cells 6 having the column number "1" and the shelf numbers "0" through "34" and writes the bar code to the respective cell position, for each cell where the fingers 4 are able to hold the magnetic tape cartridge 5.
This operation of searching for the magnetic tape cartridges 5 stored in the cells 6 having the column numbers "2" through "8" and the shelf numbers "0" through "34" is repeated. The host unit can perform the data write/read operations with respect to the mass storage unit 10 only after the above described searching operation ends.
In other words, the desired magnetic tape cartridge 5 with respect to which the data write/read is to be made is selected from the bar code based on the management information shown in FIG. 3, and the cell address of the cell 6 which stores this desired magnetic tape cartridge 5 is read out by the column number and the shelf number. The host unit instructs the mass storage unit 10 to rotate the cell drum 1 so that the cell column 15, including the cell 6 which stores the desired magnetic tape cartridge 5, confronts the accessor 2. In addition, the mass storage unit 10 is instructed to position the mechanical hand 3 to the position of the cell 6 which has the read out column number and shelf number, and to hold the desired magnetic tape cartridge 5 by the fingers 4. The mechanical hand 3 transports the desired magnetic tape cartridge 5 to the drive unit 7 or 8.
In this state, the host unit updates the management information, and erases the bar code of the cell position from which the desired magnetic tape cartridge 5 was retrieved. In addition, the host unit transports the magnetic tape cartridge 5, which is extracted from the drive unit 7 or 8, to a desired cell position to store the magnetic tape cartridge 5 in the cell 6 at this desired cell position. The host unit also writes the bar code which is read from the magnetic tape cartridge 5 which is transported to the desired cell position, so as to update the management information.
As described above, during the normal write/read operation, the host unit simply needs to update the management information every time one magnetic tape cartridge 5 is moved. For this reason, the processing time required for the updating of the management information is relatively short and the processing efficiency of the computer system is not deteriorated thereby.
However, there is no intervention by the host unit when the operator stores or retrieves the magnetic tape cartridge 5 via the open door 9. Hence, it is impossible in this case to recognize the cells 6 which change, from the state where the magnetic tape cartridge 5 is stored to the state where no magnetic tape cartridge 5 is stored or vice versa. For this reason, the host unit must carry out a process similar to that at the time of the initial setting in order to update the management information. In other words, when the end of the load/eject mode is notified from the mass storage unit 10, the host unit instructs the mass storage unit 10 to search whether or not the magnetic tape cartridge 5 is stored in the cell 6 for all of the 315 cells 6 in the cell drum 1.
The time required to search whether or not the magnetic tape cartridge 5 is stored in one cell 6 is on the order of several seconds because this time includes the time required for the accessor 2 to carry out the mechanical operations. Therefore, it takes 30 minutes or more to make the search operation with respect to all of the 315 cells 6. This time of 30 minutes or more is necessary to make the search operation, regardless of whether or not only one magnetic tape cartridge 5 is to be stored or retrieved with respect to the cell drum 1. As a result, there is a problem in that the processing efficiency of the computer system which uses the mass storage unit 10 is greatly deteriorated when the search operation is involved.